Conventionally, when an abnormality such as stenosis, occlusion or the like occurs in a lumen such as a blood vessel or the like, stent treatment has been performed by inserting the stent within the lumen and holding the lumen in an expanded state, for example. The stent overall has a tubular shape, and has a small diameter when inserted in the lumen, but is placed with the diameter enlarged within the lumen. As a method for expanding the stent within the lumen, in addition to expansion using a balloon, there is also self expansion using shape memory materials or the like, mechanical expansion, and the like.
Also, in addition to making it possible for the stent to be deformed by expansion or contraction as described above, in consideration of reducing the burden on the living body, improving biocompatibility and the like, a porous structure with many through holes provided in the peripheral wall part or a strut structure connected linearly is used. In specific terms, for example as noted in Japanese Unexamined Patent Publication No. JP-A-2007-267844 (Patent Document 1) or the like, in addition to cutting a metal tube of stainless steel, platinum or the like to a suitable length, by forming through holes or a strut using laser processing on the peripheral wall, the stent is constituted for which the strut cross section shape is a simple rectangular shape.
However, with a stent of the conventional structure for which the strut has a simple rectangular cross section shape, it was still difficult to obtain sufficient freedom of design to realize compatibility considering suitability for each patient and the like, and it was hard to say that the required characteristics at medical sites could be sufficiently handled.
In specific terms, when stent treatment is performed with a stent of the conventional structure placed at the stenosis portion of a patient with arteriosclerosis, for example, though the expanded state of the blood vessel is maintained immediately after the stent is placed, at several weeks to several months after the surgery, by a clot adhering to the stent, there were cases of restenosis occurring at the blood vessel in the position at which the stent was placed. The existence and degree of restenosis depends on things like the portion at which the stenosis occurred, the status at that stenosis portion, the patient, and the like, thus improvement and handling thereof was difficult with stents of the conventional structure.
In addition, when expanding the stent with a balloon or the like to place it within a blood vessel, there were cases when the stent had its position displaced within the blood vessel in the lengthwise direction. The existence and degree of positional displacement of the stent within the blood vessel also differs according to the site and status of the portion at which the stent was placed, the patient, and the like, so that improvement and handling thereof was also difficult with stents of the conventional structure.
Furthermore, with this kind of stent of the conventional structure, a metal tube which is an element tube has a simple, straight, round tubular shape. Thus, it was difficult to make a shape to correspond to the placement portion in a lumen such as a blood vessel or the like. Therefore, with the lumen, for example, in a portion for which the inner diameter dimension changes with a tapered shape, or a bifurcated portion such as a bifurcation or the like, there was the problem that it was difficult to prepare a stent that precisely matched the shape of the lumen.
In fact, when doing laser processing on the element tube to form through holes or a strut, when there is a large area to be cut, there is the problem that the yield becomes poor. To increase the yield, there was also the idea of taking a stent obtained by implementing laser processing on a small diameter, round tubular element tube, reducing the diameter and inserting it in the lumen, and then enlarging the diameter to be larger than the initial element tube diameter for placement. However, there was the risk that distortion and residual stress in the enlarged diameter state would become great, and it would not be possible to obtain a stable shape and durability.
Also, it is likely for roughness such as burrs to occur at the portion at which laser processing was done, meaning that post-processing either chemically or mechanically is required. This poses the problem that manufacturing becomes complex, and precise management of post-processing and the like would be difficult.